The invention pertains to a cutting insert, and in particular, to a polycrystalline diamond (PCD) cutting insert, as well as to a diamond-coated cutting insert that has an improved flank surface roughness.
In the manufacture of a polycrystalline diamond cutting insert, the PCD blank is brazed into a pocket which has been ground into the carbide substrate so as to form a PCD cutting insert. The periphery (i.e., the flank surfaces) of the PCD cutting insert is then finish-ground to the specified dimensions for a particular style of cutting insert. This grinding operation is performed in a direction which is normal (i.e., perpendicular) to the cutting edge of the PCD cutting insert. Generally speaking it is easier to grind the periphery in a direction normal to the cutting edge since the grinding proceeds from the carbide into the diamond. The flank surfaces of the PCD blank which contain the grind lines perpendicular to the cutting edge create serrations (which are typically microscopic) along the cutting edge. These serrations adversely affect the surface finish of the workpiece produced by the PCD cutting insert. Because the lay of the grind lines is normal to the cutting edge, it is very difficult to polish out these serrations to achieve a flank surface with a mirror finish (i.e., less than 5 microinches, R.sub.a) In the absence of a flank surface with a; mirror finish the PCD cutting insert cannot produce an optimum workpiece surface finish wherein the workpiece surface finish approaches (or even attains) the theoretical value.
It thus becomes apparent that it would be highly desirable to provide a PCD cutting insert which has a flank surface with a mirror finish of less than 5 microinches, R.sub.a. It would also be very desirable to provide a PCD cutting insert which produces a workpiece with a surface finish that approaches (or possibly reaches) the theoretical value for the workpiece surface finish.
At the present time there is a diamond coated cutting insert which presents a rake surface which has a predetermined surface roughness. U.S. Pat. No. 5,585,176 to Grab et al. for DIAMOND COATED TOOLS AND WEAR PARTS (which is hereby incorporated by reference herein), as well as U.S. Pat. No. 5,648,119 to Grab et al. for PROCESS FOR MAKING DIAMOND COATED TOOLS AND WEAR PARTS (which is hereby incorporated by reference herein), describes such a diamond coated cutting insert and the process to make such a cutting insert. In addition, U.S. Pat. No. 5,709,907 to Battaglia et al. for a METHOD OF MAKING COATED CUTTING TOOLS (which is hereby incorporated by reference herein) and U.S. Pat. No. 5,722,803 to Battaglia et al. for a CUTTING TOOL AND METHOD OF MAKING THE CUTTING TOOL (which is hereby incorporated by reference herein) each describe a diamond coated cutting insert with a substrate having a roughened rake surface so as to provide for microscopic chip control. By having a substrate rake surface with this surface roughness, the diamond coated cutting inserts provide for a certain degree of chip control so that long coils of metal do not form, but instead, shorter chips form during a metal removal operation due to the presence of the surface roughness on the rake surface. Disadvantages associated with the formation of long coils of metal (i.e., "birds nests") during the cutting operation are set forth in U.S. Pat. No. 5,709,907 and U.S. Pat. No. 5,722,803.
By providing a PCD cutting insert wherein the rake surface of the PCD blank has a surface roughness of a magnitude like those set forth in U.S. Pat. No. 5,585,176 to Grab et al., U.S. Pat. No. 5,648,119 to Grab et al., U.S. Pat. No. 5,709,907 and U.S. Pat. No. 5,722,803, the PCD cutting insert would provide for microscopic chip control. It is therefore apparent that it would be desirable to provide a PCD cutting insert wherein the PCD blank presents a rake surface with a surface roughness that provides for microscopic chip control and a flank surface that has a mirror finish (less than 5 microinches, R.sub.a). Such a PCD cutting insert would provide for optimum chip control as well as provide a workpiece surface finish that approaches (or possibly attains) the theoretical value.
Referring to a diamond coated cutting insert, it would also be highly desirable to provide a diamond coated cutting insert which has a roughened rake surface and a flank surface with a mirror finish (less than five microinches, Ra). Such a diamond coated cutting insert would provide for optimum chip control as well as provide a workpiece surface finish that approaches (or possibly attains) the theoretical value.